"The kids have known we were getting married since we got engaged," Rimes tells PEOPLE of Cibrian's sons Mason, 7, and Jake, 4, from his first marriage. "We explained that they were going to have two families."

Adds Cibrian, 37, "The kids come first in everything we do. We wanted to make sure LeAnn and my wedding was not only ours, but their party too. They were beyond excited to celebrate us all coming together as a family."

Preparing the boys for the steps ahead wasn't something the newlyweds took lightly. The couple went to therapy to figure out which words to use and how to talk to Mason and Jake about such a big concept.

"It was really important for us to figure out how to explain it," says Rimes, 28, who calls herself a "bonus mom." "And they were great. They were super excited and wanted to know what they could do."

The night before the ceremony, the couple took the boys to the wedding site to show them how things had been set up for the party – which included light sabers and a Star Wars-themed table for Mason, Jake and two of their closest friends.

"They were at the forefront of our minds the whole time," says Rimes, whose stepsons call her "Le." "I've always felt an overwhelming sense of responsibility to them. But in that moment when I looked down at them, when we were saying our vows, it became more real than it had ever been. They don't have to be my blood children to be truly loved."